1. Field of the Invention
The present invention relates to a regulating check valve that is used in high-pressure equipment and also relates to a fuel injection valve that has the regulating check valve and injects high-pressure fuel into an internal combustion engine.
2. Description of Related Art
It has been demanded in recent years that fuel injection valves for injecting high-pressure fuel into internal combustion engines adjust fuel injection quantity with quite high accuracy and respond promptly to control commands. This is for reducing emissions in the combusted exhaust gas and for improving gas mileage, from the standpoint of environmental protection. To these demands for improving the accuracy of the fuel injection operation and the response of the fuel injection valve, various fuel injection valves that are driven by piezoelectric actuators are proposed. The fuel injection valve driven by the piezoelectric actuator can generate a large force and has a fine response with respect to a conventional fuel injection valve driven by a solenoid.
JP2006-214317A discloses a fuel injection valve in which a needle slides in a fuel injection valve body in its axial direction. The needle has a tip portion, which opens an injection hole to an injection pressure passage or closes the injection hole from the injection pressure passage, and a large-diameter base portion, which is formed on an opposite side of the tip portion. A step surface on one axial end of the large-diameter portion is exposed to a control pressure chamber. A piezoelectric actuator moves a pressurizing piston to make fuel pressure in the control pressure chamber larger than fuel injection pressure. Thereby, the needle is pushed upward to open the injection hole to the injection pressure passage. The other axial end of the large-diameter portion is exposed to a back pressure chamber. The back pressure chamber is opened to the injection pressure passage.
In such a fuel injection valve, the piezoelectric actuator extends when it receives an injection signal, and the fuel pressure in the control pressure chamber increases in accordance with a displacement of the pressurizing piston that is moved by the piezoelectric actuator. Thereby, the needle is pushed upward by the fuel pressure in the control pressure chamber, and the injection hole is opened to start fuel injection. A distal end surface of the pressurizing piston is exposed to a piston chamber that is communicated to the injection pressure passage and to the back pressure chamber via a check valve. When the fuel injection is performed, the check valve closes to maintain increased fuel pressure in the control pressure chamber and to prevent a backflow of the fuel from the control pressure chamber into the back pressure chamber. After the fuel injection is stopped, the check valve opens to supply the fuel from the injection pressure passage to the control chamber because the fuel in the control chamber decreases due to fuel leakage at a sliding surface of the large-diameter portion.
JP9-170514A corresponding to U.S. Pat. No. 5,752,486 discloses a technique for inhibiting pulsations of fuel pressure in a fuel passage between a common rail and fuel injection valves. In this technique, a narrow passage is provided at a point where the common rail and the fuel passage is connected, to inhibit the pulsation of the fuel pressure due to propagation of water hammer that is caused by discharges of high-pressure fuel from a high-pressure supply pump and/or by injections of the high-pressure fuel from fuel injection valves.
However, in such a fuel injection valve as disclosed in JP2006-214317A, the control pressure chamber is communicated to the injection pressure passage and to the back pressure passage via the check valve having a conventional construction. Therefore, while the fuel pressure in the control pressure chamber is larger than the fuel pressure in the injection pressure passage and in the back pressure chamber, the check valve keeps closing, to prevent the backflow of the fuel from the control pressure chamber to the back pressure chamber. If the fuel pressure abruptly drops just after the fuel injection, valve-closing pressure acting on a rear surface of the needle can become relatively smaller than the fuel pressure in the control pressure chamber. Accordingly, even though the piezoelectric actuator is not driving, the needle can be pushed upward in a valve-opening direction by the fuel pressure in the control pressure chamber, and the fuel can be injected inappropriately.
Moreover, the abrupt change of the fuel pressure, which is caused by the fuel injection, can generate a shock wave that propagates in a fuel supply pipe at the velocity of sound. Then, the reflected wave of the shock wave can cause pulsation of the fuel pressure in the fuel supply pipe. In the conventional fuel injection valve, the check valve keeps closing even when fuel supply pressure is temporarily decreased due to such a pulsation. Thereby, the fuel pressure in the control pressure chamber can become relatively larger than the fuel pressure in the injection pressure chamber and in the back pressure chamber, and the fuel can be injected regardless of the operation of the piezoelectric actuator.
As in JP9-170514A corresponding to U.S. Pat. No. 5,752,486, in such a case that the narrow passage is provided at the point where the common rail and the fuel passage is connected to inhibit the pulsation of the fuel pressure, it is possible to avoid the influence of the pulsation in the high-pressure fuel supply passage. However, this construction can decrease actual fuel injection pressure because of pressure decrease at the narrow passage.